Resolver

ABSTRACT

Disclosed is a resolver robust against external noise and having a reduced error in the detection of a rotation angle, which includes a stator made of a magnetic material and having a plurality of teeth and a plurality of slots alternately formed at an inner side thereof, insulation covers respectively having a tooth insulating unit formed at an inner side thereof corresponding to the teeth and mounted to the stator at both upper and lower surfaces of the stator, and coils wound on the teeth with the tooth insulating unit being interposed therebetween, wherein regarding winding widths of coils located at an outermost circumference among the wound coils, a ratio of a shortest winding width to a longest winding width is 0.69 or above and 1 or below.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase application of PCT Application No.PCT/KR2015/014435, filed on Dec. 29, 2015, which claims the benefit andpriority to Korean Patent Application No. 10-2015-0159831, filed Nov.13, 2015. The entire disclosures of the applications identified in thisparagraph are incorporated herein by references.

TECHNICAL FIELD

The present disclosure relates to a device for detecting a rotationangle of a rotating device, and more particularly, to a resolver.

BACKGROUND

When controlling a rotating device, for example a motor, rotationinformation should be detected precisely and rapidly. When controlling arotating device, a movement or rotating location of a rotating bodyshould be measured accurately by means of a rotation angle detectingdevice installed at a rotary shaft. A resolver and an encoder have beenadopted and used for such measurement, and these detecting devices haveadvantages and disadvantages. The resolver directly detects an absolutelocation of a rotor and calculates a rotating direction and a rotatingspeed by means of the change of location of the rotor.

An electric power steering (EPS) is used for a vehicle in order toassist the operation of a handle by driving a motor with a battery. Theelectric power steering receives attention as an efficient system with aless power loss of an engine, in comparison to a case where a hydraulicpressure is generated by means of a rotating force of an engine. Sincethe EPS needs precise control, a rotation angle detecting device forprecisely detecting a rotation angle of the motor is required, and therotation angle detecting device demands high reliability. As such arotation angle detecting device for a vehicle, a resolver having higherenvironment resistance in comparison to an encoder is used.

The resolver is a kind of sensor for precisely measuring a rotatingspeed and a rotation angle of a motor. Generally, the resolver has arelatively simple structure in which both an excitation coil and anoutput coil are located at a stator and an oval or multi-pole rotor islocated at an inner side of the stator. A resolver having this structureis disclosed in Japanese Unexamined Patent Publication No. 1996-178610.

FIG. 1 is a diagram in the above Japanese Unexamined Patent Publication,and a resolver includes a rotor 10 having a rotary shaft providedtherethrough and a ring-shaped stator 11 configured to face the rotor 10with a gap. The rotor 10 has a plurality of salient poles 10 a formedalong an outer circumference thereof, and the ring-shaped stator 11 hasa plurality of teeth 11 b and a plurality of slots 11 a alternatelyformed along an inner circumference thereof. In addition, an excitationcoil and an output coil are wound on the teeth 11 b of the stator 11,and the excitation coil and the output coil are accommodated in theslots 11 a. Here, the output coil is composed of a first output coil anda second output coil. If an excitation power is applied to theexcitation coil and the rotary shaft is rotated, a sine signal and acosine signal are output from the first output coil and the secondoutput coil, and a rotation angle of the resolver may be known byanalyzing the signals.

As described above, in the resolver, the coils wound on the teeth 11 bof the stator 11 is an important element for inputting and outputtingsignals, and thus a precise design is demanded when winding the coils ata rotation angle detecting device such as a resolver. For example, whenthe coil is wound, if the coil is would irregularly, a high-frequencywave may be generated at an outer waveform, or electric interference maybe caused between coils wound on two adjacent teeth 11 b, therebygenerating an error in detecting a rotation angle. In addition, if acoil is wound more on the teeth 11 b, an area occupied by the coil atthe slot 11 a between the teeth 11 b increases, which causes electricinterference between coils wound on two adjacent teeth 11 b and resultsin an error. If a coil is wound less on the teeth 11 b, a transformationratio of an induced voltage of the output coil is lowered, which becomesvulnerable to external noise.

Patent Literature: Japanese Unexamined Patent Publication No.1996-178610

DISCLOSURE Technical Problem

The present disclosure is designed according such a technical demand,and therefore the present disclosure is directed to providing a resolverwhich is robust against external noise and has a reduced error in thedetection of a rotation angle.

Technical Solution

In one aspect of the present disclosure, there is provided a resolver,comprising: a stator made of a magnetic material and having a pluralityof teeth and a plurality of slots alternately formed at an inner sidethereof; insulation covers respectively having a tooth insulating unitformed at an inner side thereof corresponding to the teeth and mountedto the stator at both upper and lower surfaces of the stator; and coilswound on the teeth with the tooth insulating unit being interposedtherebetween, wherein regarding winding widths of coils located at anoutermost circumference among the wound coils, a ratio of a shortestwinding width to a longest winding width is 0.69 or above and 1 orbelow.

The ratio of the shortest winding width to the longest winding widthamong the wound coils may be 0.8 or above and 1 or below.

A coil occupying ratio per slot, which is defined by the followingequation and represents a ratio of area occupied by the coils in a slotto which the insulation covers are fixed, may be 35% or below:

EquationCoil occupying ratio per slot=(area occupied by coils in a singleslot)/(area of a single slot).

The coil occupying ratio per slot may be 3% or above.

In a slot to which the insulation covers are fixed, a shortest distancebetween coils wound on two teeth adjacent to each other may be 4 mm orabove.

The resolver may further comprise a rotor made of a magnetic materialand configured to rotate based on a rotary shaft to change a gappermeance together with the stator.

The rotor may be an inner-type rotor disposed at an inner center of thestator.

The rotor and the stator may be formed by laminating a plurality ofmagnetic steel plates with a predetermined thickness.

The stator may be formed by manufacturing the magnetic steel plates intoa ring shape having a plurality of teeth and a plurality of slotsalternately formed at an inner side thereof and then laminating themagnetic steel plates.

The rotor may be ring-shaped having a through hole formed at a centerportion thereof so that the rotary shaft is inserted therein and aplurality of salient poles formed at an outer circumference thereof tochange the gap permeance.

The salient pole may have an arc shape with a diameter smaller than atleast a diameter of the rotor.

A center of the arc may be disposed spaced apart from a center of therotor by a predetermined distance, and the arcs of the plurality ofsalient poles have the same diameter.

In another aspect of the present disclosure, there is also provided aresolver, comprising: a stator made of a magnetic material and having aplurality of teeth and a plurality of slots alternately formed at aninner side thereof; insulation covers respectively having a toothinsulating unit formed at an inner side thereof corresponding to theteeth and mounted to the stator at both upper and lower surfaces of thestator; and coils wound on the teeth with the tooth insulating unitbeing interposed therebetween, wherein regarding winding widths of coilslocated at an outermost circumference among the wound coils, a ratio ofa mean winding width of the coils located at the outermost circumferenceto a longest winding width is 0.83 or above and 1 or below, and whereinregarding the winding widths of the coils located at the outermostcircumference among the wound coils, a ratio of the mean winding widthof the coils located at the outermost circumference to a shortestwinding width is 1 or above and 1.16 or below.

Regarding the winding widths of the coils located at the outermostcircumference among the wound coils, a ratio of the shortest windingwidth to the longest winding width may be 0.69 or above and 1 or below.

Regarding the winding widths of the coils located at the outermostcircumference among the wound coils, a ratio of the mean winding widthof the coils located at the outermost circumference to the longestwinding width may be 0.89 or above and 1 or below, and regarding thewinding widths of the coils located at the outermost circumference amongthe wound coils, a ratio of the mean winding width of the coils locatedat the outermost circumference to the shortest winding width may be 1 orabove and 1.1 or below.

Regarding the winding widths of the coils located at the outermostcircumference among the wound coils, a ratio of the shortest windingwidth to the longest winding width may be 0.8 or above and 1 or below.

A coil occupying ratio per slot, which is defined by the followingequation and represents a ratio of area occupied by the coils in a slotto which the insulation covers are fixed, may be 35% or below:

EquationCoil occupying ratio per slot=(area occupied by coils in a singleslot)/(area of a single slot).

The coil occupying ratio per slot may be 3% or above.

In a slot to which the insulation covers are fixed, a shortest distancebetween coils wound on two teeth adjacent to each other may be 4 mm orabove.

The resolver may further comprise a rotor made of a magnetic materialand configured to rotate based on a rotary shaft to change a gappermeance together with the stator.

The rotor may be an inner-type rotor disposed at an inner center of thestator.

The rotor and the stator may be formed by laminating a plurality ofmagnetic steel plates with a predetermined thickness.

The stator may be formed by manufacturing the magnetic steel plates intoa ring shape having a plurality of teeth and a plurality of slotsalternately formed at an inner side thereof and then laminating themagnetic steel plates.

The rotor may be ring-shaped having a through hole formed at a centerportion thereof so that the rotary shaft is inserted therein and aplurality of salient poles formed at an outer circumference thereof tochange the gap permeance.

The salient pole may have an arc shape with a diameter smaller than atleast a diameter of the rotor.

A center of the arc may be disposed spaced apart from a center of therotor by a predetermined distance, and the arcs of the plurality ofsalient poles have the same diameter.

Advantageous Effects

The resolver of the present disclosure may precisely measures a rotationangle of a rotating device such as a motor since the resolver is robustagainst external noise and has an output waveform of enhanced accuracy.

The resolver of the present disclosure may have improved productperformance by reducing interference between magnetic fluxes generatedat adjacent teeth.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a resolver in the related art.

FIG. 2 is a perspective view showing a resolver according to anembodiment of the present disclosure.

FIG. 3 is a partial plane view showing the resolver of FIG. 2.

FIG. 4 is a diagram showing a rotor of the resolver according to anembodiment of the present disclosure.

FIG. 5 is a partial horizontal sectional view showing a resolveraccording to an embodiment of the present disclosure, which depicts awound shape of a coil.

FIG. 6 is a partial horizontal sectional view showing a resolveraccording to an embodiment of the present disclosure, for illustrating awinding width.

FIG. 7 is a diagram showing a test environment of the resolver accordingto an embodiment of the present disclosure.

FIG. 8 is a graph showing a maximum error rate of each sample resolveraccording to a l_(min)/l_(max) ratio.

FIG. 9 is a graph showing a maximum error rate of each sample resolveraccording to a l_(mean)/l_(max) ratio.

FIG. 10 is a graph showing a maximum error rate of each sample resolveraccording to a l_(mean)/l_(min) ratio.

FIG. 11 is an enlarged view showing a portion A of FIG. 3.

FIG. 12 is a diagram for illustrating a shortest distance between coilsaccording to an embodiment of the present disclosure.

FIGS. 13, 14, 15, 16, 17, 18, 19, 20 and 21 are graphs showing an errorrate of each resolver prepared as a sample.

BEST MODE

The above objects, features and advantages of the present disclosurewill become apparent from the following descriptions of the embodimentswith reference to the accompanying drawings, from which it will bedeemed that a person having ordinary skill can easily practice thetechnical features of the present disclosure. Also, any explanation ofthe prior art known to relate to the present disclosure may be omittedif it is regarded to render the subject matter of the present disclosurevague. Hereinafter, an embodiment of the present disclosure will bedescribed in detail with reference to the accompanying drawings.

FIG. 2 is a perspective view showing a resolver according to anembodiment of the present disclosure, FIG. 3 is a partial plane viewshowing the resolver of FIG. 2, and FIG. 4 is a diagram showing a rotorof the resolver according to an embodiment of the present disclosure.

Referring to FIGS. 2, 3 and 4, a resolver of this embodiment includes arotor 300, a stator 110 made of a magnetic material and having aplurality of teeth 111 and a plurality of slots 112 alternately formedalong an inner circumference thereof, ring-shaped insulation covers 120mounted to both upper and lower surfaces of the stator 110, and coils140 respectively wound on the teeth 111 with the insulation cover 120being interposed therebetween.

The rotor 300 is a ring-shaped ferromagnetic body having a through hole301 formed at center portion thereof so that a rotary shaft is insertedthrough the through hole 301. The rotor 300 may be formed by laminatingmagnetic steel plates of a predetermined thickness. The rotor 300 servesas an inner-type ferromagnetic body disposed at an inner center of thestator 110 and has a plurality of salient poles formed along an outercircumference thereof to transform a gap permeance together with thestator 110 while rotating based on the rotary shaft. At this time, thesalient pole of the rotor 300 has an arc shape having a diameter R2smaller than a diameter R1 of the rotor 300. A center C2 of the arc ofthe salient pole is disposed spaced apart from a center C1 of the rotor300 by a predetermined distance, and the diameter R2 of the arc of eachsalient pole may be identical to each other.

The stator 110 is a ring-shaped ferromagnetic body having a plurality ofteeth 111 formed along an inner circumference thereof to face the rotor300 with a gap and slots 112 between adjacent teeth 111. The stator 110may be prepared by manufacturing magnetic steel plates into a ring shapehaving a plurality of teeth 111 and a plurality of slots 112 alternatelyformed at an inner side thereof and laminating the magnetic steelplates.

The insulation covers 120 are mounted to both upper and lower surfacesof the stator 110 and are composed of an upper insulation cover and alower insulation cover. The insulation cover 120 has a plurality oftooth insulating units 121 formed to cover the teeth 111 of the stator110 at regular intervals along an inner circumference thereof. Since theinsulation covers 120 are mounted to both upper and lower surfaces ofthe stator 110, the tooth insulating units 121 cover the upper and lowersurfaces of the teeth 111.

In a state where the insulation covers 120 are mounted and fixed to bothupper and lower surfaces of the stator 110, the coils 140 are wound onthe tooth insulating units 121. In other words, the coil 140 is wound onthe teeth 111 with the tooth insulating unit 121 being interposedtherebetween, without directly contacting the teeth 111. Since the coil140 is wound on the teeth 111 with the tooth insulating unit 121 beinginterposed therebetween, the coil 140 is accommodated in the slot 112.The coil may be composed of a one-phase excitation coil and two-phaseoutput coils. One output coil of the two-phase output coils outputs aSIN signal, and the other output coil outputs a COS signal. If anexcitation voltage is applied to the excitation coil and the rotaryshaft is rotated, the first output coil and the second output coiloutputs a sine signal and a cosine signal, and a rotation angle of theresolver may be known by analyzing the signals.

In the resolver, when a coil is wound on the teeth 111 by means of thetooth insulating unit 121, the coil may be wound in various shapes. FIG.5 is a partial horizontal sectional view showing a resolver according toan embodiment of the present disclosure, which depicts a wound shape ofa coil. Here, (a) of FIG. 5 depicts that the coils accommodated in theslot 112 has a trapezoidal shape in the slot 112, (b) of FIG. 5 showsthat the coils accommodated in the slot 112 has a rectangular shape inthe slot 112. In addition, coils may be wound on the teeth 111 invarious shapes.

In the resolver as described above, the coils should be wound uniformlyon the teeth 111 by means of the tooth insulating unit 121. If the coilsare wound irregularly, a high-frequency wave may be generated at anouter waveform, or electric interference may be caused between coilswound on two adjacent teeth 111, thereby generating an error indetecting a rotation angle. Parameters for evaluating uniformity ofwound coils may be defined as follows.

FIG. 6 is a partial horizontal sectional view showing a resolveraccording to an embodiment of the present disclosure, for illustrating awinding width. In FIG. 6, a coil at an outermost circumference isdepicted among the coils wound on the teeth 111 by means of the toothinsulating unit 121. (a) of FIG. 6 depicts a case where coils are woundin a rectangular shape, (b) FIG. 6 depicts a case where coils are woundin a trapezoidal shape, and (c) of FIG. 6 depicts a case where coils arewound with a convex center.

Referring to FIG. 6, coils wound on the teeth 111 at an outermostcircumference respectively have winding widths of l₁, l₂ . . . l_(n), ina radial direction. At this time, the winding width means a length of acoil which extends out vertically from the slot 112, cross the toothinsulating unit 121 and come into an adjacent slot 112 vertically. Basedon a section of a coil, a start point and an end point of the coil maybe set from a center of the coil or from an outer circumference of thecoil. In this embodiment, the start point and the end point of the coilare set based on the center of the coil. From the winding widths of thecoils, three parameters are defined. In other words, (1) al_(mean)/l_(max) ratio, (2) a l_(mean)/l_(min) ratio, and (3) al_(min)/l_(max) ratio are defined. l_(mean) represents a mean of windingwidths (l₁, l₂ . . . l_(n)) of coils, l_(max) represents a longestwinding width among winding widths (l₁, l₂ . . . l_(n)) of coils, andl_(min) represents a shortest winding width among winding widths (l₁, l₂. . . l_(n)) of coils.

The l_(min)/l_(max) ratio is a ratio between a shortest winding widthand a longest winding width. If the l_(min)/l_(max) ratio is 1, thismeans that all winding widths are equal to each other and thus coils arewound uniformly. If the l_(min)/l_(max) ratio is smaller than 1, thismeans that coils are wound more irregularly. The l_(mean)/l_(max) ratiois a ratio between a mean of the winding widths and a longest windingwidth, and the l_(mean)/l_(min) ratio is a ratio between a mean of thewinding widths and a shortest winding width. If both thel_(mean)/l_(max) ratio and the l_(mean)/l_(min) ratio are 1, this meansthat all winding widths are equal to each other and thus coils are wounduniformly. If the l_(mean)/l_(max) ratio and the l_(mean)/l_(min) ratioare smaller than 1, this means that coils are wound more irregularly.Therefore, the uniformity of wound coils of the resolver may beevaluated by using the l_(min)/l_(max) ratio, or by using thel_(mean)/l_(max) ratio and the l_(mean)/l_(min) ratio.

Generally, the resolver is demanded to have an error rate of 0.5 orbelow. First, when the l_(min)/l_(max) ratio is used as a basis, if thel_(min)/l_(max) ratio is 0.69 or above and 1 or below, the error ratebecomes 0.5 or below. Next, when the l_(mean)/l_(max) ratio and thel_(mean)/l_(min) ratio are used as a basis, if the l_(mean)/l_(max)ratio is 0.83 or above and 1 or below and the l_(mean)/l_(min) ratio is1 or above and 1.16 or below, the error rate becomes 0.5 or below.Preferably, when the l_(min)/l_(max) ratio is used as a basis, it isdesirable that the l_(min)/l_(max) ratio is 0.8 or above and 1 or below.If the l_(min)/l_(max) ratio is lower than 0.8, the error rate increasesabruptly in comparison to a case where the l_(min)/l_(max) ratio is 0.8or above. Therefore, in order to operate the resolver stably, it is mostdesirable that the l_(min)/l_(max) ratio is 0.8 or above and 1 or below.When the l_(mean)/l_(max) ratio and the l_(mean)/l_(min) ratio are usedas a basis, it is most desirable that the l_(mean)/l_(max) ratio is 0.89or above and 1 or below, and the l_(mean)/l_(min) ratio is 1 or aboveand 1.1 or below.

Hereinafter, results of the performance test of a resolver according tothe uniformity of wounded coils will be described with reference toTable 1 below.

Preparation of Samples

A stator 110 having twenty-four slots 112, insulation covers 120, arotor 300 having eight salient poles and coils 140 are prepared. At thistime, the stator 110 and the rotor 300 are ferromagnetic bodies withhigh magnetic permeability and are manufactured by laminating steelplates with a thickness of 0.5 mm in order to reduce a core loss. Afterthe stator 110 and the insulation cover 120 are assembled, an excitationcoil and an output coil are wound on each slot 112 by means of acircular winding machine to fabricate a resolver. 14 resolvers wereprepared by designating a coil diameter of 0.15 mm a winding pitch of0.1555 mm and changing a winding shape of the coils variously. If thecoils have a trapezoidal winding shape, when a first coil is wound, awinding start point and a winding end point are set to a start point andan end point of the slot 112, and the winding start point is changedfrom a second coil, while the winding end point is maintainedidentically. If the coils have a convex winding shape, when a first coilis wound, a winding start point and a winding end point are set to astart point and an end point of the slot 112, and the winding startpoint and the winding end point are changed from a second coil.

Measurement of an Error Rate

FIG. 7 is a diagram showing a test environment of the resolver accordingto an embodiment of the present disclosure. After each resolver isprepared as described above in relation to sample preparation, eachresolver 630 is coupled to one end of a rotary shaft of a motor 610, andan encoder 620 is coupled to the other end of the rotary shaft. Inaddition, a calculator 640 analyzes output waveforms of the resolver 630and the encoder 620. In detail, after the rotary shaft of the motor 610is operated, the calculator 640 calculates a rotation angle profile byanalyzing the output waveform of the resolver 630 and calculates anerror rate by comparing the rotation angle profile with a rotation angleprofile of the encoder 620. Each resolver 630 is tested ten times, amongwhich a greatest error rate is defined as a maximum error rate.Generally, the resolver is demanded to have a maximum error rate of 0.5or below. The winding width of the coil is checked by means of x-rayinspection.

TABLE 1 maximum l_(mean)/_(lmax) l_(mean)/l_(min) l_(min)/l_(max) errorrate Example 1 0.993 1.005 0.982 0.258 Example 2 0.975 1.023 0.954 0.263Example 3 0.952 1.049 0.916 0.265 Example 4 0.937 1.061 0.886 0.272Example 5 0.929 1.07 0.851 0.275 Example 6 0.91 1.089 0.825 0.288Example 7 0.892 1.099 0.803 0.298 Example 8 0.875 1.109 0.759 0.352Example 9 0.858 1.149 0.72 0.412 Example 10 0.841 1.152 0.698 0.475Comparative Example 1 0.824 1.178 0.649 0.525 Comparative Example 20.802 1.195 0.612 0.567 Comparative Example 3 0.795 1.207 0.588 0.602Comparative Example 4 0.773 1.229 0.543 0.627

FIG. 8 is a graph showing a maximum error rate of each sample resolveraccording to l_(min)/l_(max) ratio, FIG. 9 is a graph showing a maximumerror rate of each sample resolver according to l_(mean)/l_(max) ratio,and FIG. 10 is a graph showing a maximum error rate of each sampleresolver according to l_(mean)/l_(min) ratio. In other words, FIGS. 8, 9and 10 express Table 1 with graphs.

Referring to Examples 1 to 10 of Table 1 and FIG. 8, when thel_(min)/l_(max) ratio is used as a basis, if the l_(min)/l_(max) ratiois 0.69 or above and 1 or below, the maximum error rate is 0.5 or below.Next, Referring to Table 1 and FIGS. 9 and 10, when the l_(mean)/l_(max)ratio and the l_(mean)/l_(min) ratio are used as a basis, if thel_(mean)/l_(max) ratio is 0.83 or above and 1 or below and thel_(mean)/l_(min) ratio is 1 or above and 1.16 or below, the maximumerror rate is 0.5 or below. Meanwhile, seeing Comparative Examples 1 to4, if the above ratio condition is not satisfied, the maximum error rateis greater than 0.5.

Meanwhile, in Examples 1 to 7, the error rate increases as much as0.0057 on average, but in Examples 8 to 10, the error rate increases asmuch as 0.03075 on average. This is because, when the l_(min)/l_(max)ratio is smaller than 0.8, the error rate increases more greatly incomparison to a case where the l_(min)/l_(max) ratio is 0.8 or above.Therefore, in order to operate the resolver stably, it is most desirablethat the l_(min)/l_(max) ratio is 0.8 or above and 1 or below. Inaddition, when the l_(mean)/l_(max) ratio and the l_(mean)/l_(min) ratioare used as a basis, it is most desirable that the l_(mean)/l_(max)ratio is 0.89 or above and 1 or below, and the l_(mean)/l_(min) ratio is1 or above and 1.1 or below.

Meanwhile, in this resolver, when the coil is wound on the teeth 111with the tooth insulating unit 121 being interposed therebetween andaccommodated in the slot 112 in a state where the insulation cover 120is fixed, a coil occupying ratio per slot, which represents a ratio ofarea occupied by coils in an area of a single slot 112, gives a seriousinfluence on the performance of the resolver. The coil occupying ratioper slot may be expressed as in Equation 1 below.Coil occupying ratio per slot=(area occupied by coils in a singleslot)/(area of a single slot)  Equation 1

The occupying ratio will be described below in more detail. FIG. 11 isan enlarged view showing a portion A of FIG. 3.

As described above, the plurality of teeth 111 and the plurality ofslots 112 are alternately formed along the inner circumference of thestator 110. In addition, the insulation covers 120 are mounted and fixedto both upper and lower surfaces of the stator 110. The tooth insulatingunits 121 corresponding to the teeth 111 of the stator 110 are formed atthe inner circumference of the insulation cover 120 to cover each tooth11 of the stator 110 at both upper and lower surfaces thereof. At thistime, when being observed on a plane, the tooth insulating unit 121covering the teeth 111 is slightly greater than the teeth 111.

In other words, as shown in FIG. 11, the tooth insulating unit 121 mayhave a width margin (α) so that its width is slightly greater than thewidth of the teeth 111. Therefore, in this embodiment and the appendedclaims, the area of the slot 112 may be understood as an area from whichan area of the width margin is excluded. In other words, in thisembodiment, an area of a single slot 112 is not an area between twoadjacent teeth 111 but an area between two adjacent tooth insulatingunits 121. In addition, an area of a single slot 111 is an area of afigure whose vertices correspond to four points (a, b, c, d) of twoadjacent tooth insulating units 121 as depicted in FIG. 11.

In the area of the slot 112, an area occupied by the coils 140 may beobtained with the number of turns of the coils 140 and a diameter ofeach coil 140. For example, if the excitation coil turns by an n numberand the output coil turns by a m number at each of two adjacent toothinsulating units 121 (it is assumed that the first output coil and thesecond output coil have the same radius), an area of the coils 140accommodated in the slot 112 between the two tooth insulating units 121may be obtained as in Equation 2 below.Area of coil=2nπr ₁ ²+4mπr ₂ ²  Equation 2

Here, r₁ represents a radius of the excitation coil, and r₂ represents aradius of the output coil.

Generally, a minimum number of turns of the output coil required whenthe excitation coil is wound on the tooth insulating unit 121 may beobtained as in Equation 3 below. In Equation 3, a represents the numberof turns of the excitation coil, b represents a transformation ratio, crepresents a minimum air gap between the stator and the rotor, drepresents a sectional area of each coil, and e represents an inputvoltage.

$\begin{matrix}{{{Minimum}\mspace{14mu}{number}\mspace{14mu}{of}\mspace{14mu}{turns}\mspace{14mu}{of}\mspace{14mu}{output}\mspace{14mu}{c{oil}}} = {\frac{a}{1 - b} \times c \times b \times e \times \frac{1}{d \times 100}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

Generally, the input voltage input to the excitation coil is at least 4Vrms and has a frequency of 10 kHz. At this time, the magnetic fluxdensities of the stator and the rotor serving as ferromagnetic bodiesshould not be saturated, and thus a maximum magnitude of the inputcurrent input to the excitation coil is 0.5 A. If a minimum number ofturns of the excitation coil is determined to satisfy this condition, aminimum number of turns of the output coil is determined according toEquation 3. If an occupying ratio is calculated using the determinednumber of turns of the excitation coil and the output coil, the radii ofthe excitation coil and the output coil, and the area of the slot 112between the tooth insulating units 121, it becomes a minimum occupyingratio, and this minimum occupying ratio is 3%. In other words, if thecoil occupying ratio in the slot 112 becomes smaller than 3%, the inputcurrent input to the excitation coil increases and thus gives damage toa circuit which applies the input voltage, and also the magnetic fluxdensity increases to distort a waveform of the output voltage, namelythe induced voltage. In addition, the transformation ratio of theinduced voltage generated at the output coil is lowered, thereby beingvulnerable to external noise. Therefore, the coil occupying ratio perslot should be at least 3%.

The magnetic flux generated by the input current input to the excitationcoil interlinks the output coil to generate an induced voltage. Thenormal magnetic flux generated by the input current is linked to therotor. At this time, the magnetic flux generated by the input current islinked to the rotor to generate an eddy current, and the eddy current isgenerated in a direction opposite to the normal input magnetic flux. Inaddition, the magnetic flux components generated by the induced voltagesgenerated at the first output coil and the second output coil collidewith each other to give an influence to each other. As described above,the eddy current and the magnetic flux component generated by theinduced voltage of the output coil distort the induced voltage of theoutput part to deteriorate the performance of the resolver. In order tominimize such distortion of the induced voltage at the output side, thecoil occupying ratio per slot should be 35% or below.

In other words, the distortion of performance of the resolver may bereduced when the coil occupying ratio per slot is in the range of 3% to35%.

Meanwhile, the magnetic flux may flow smoothly when a certain distanceis maintained between the coil wound on a first tooth of two adjacentteeth 111 and a coil wound on a second tooth thereof. If the distancebetween the coil wound on the first tooth of two adjacent teeth 111 andthe coil wound on the second tooth thereof is smaller, the magneticfluxes respectively generated at the teeth 111 may interfere each other,which may cause distortion of an output waveform and thus generate anerror in detecting a rotation angle. In order to reduce such an error,in the slot 112, a certain distance should be ensured between coilswound on two adjacent teeth 111, and a shortest distance between thecoils should be 4 mm or above. FIG. 12 is a diagram showing a shortestdistance (l_(min)) between the coils according to an embodiment of thepresent disclosure.

Hereinafter, results of the performance test of a resolver according tothe coil occupying ratio per slot and the shortest distance betweencoils will be described with reference to Table 2 below.

Preparation of Samples

A stator 110 having twenty-four slots 112, insulation covers 120, arotor 300 having eight salient poles and coils 140 are prepared. At thistime, the stator 110 and the rotor 300 are ferromagnetic bodies withhigh magnetic permeability and are manufactured by laminating steelplates with a thickness of 0.5 mm in order to reduce a core loss. Afterthe stator 110 and the insulation cover 120 are assembled, an excitationcoil and an output coil are wound on each slot 112 by means of acircular winding machine to fabricate a resolver. Nine resolvers areprepared in total, and each resolver is fabricated to have an occupyingratio and a shortest distance between coils as in Table 2 below.

Measurement of an Error Rate

The test environment is identical to FIG. 7 described above. After eachresolver is prepared as described above in relation to samplepreparation, each resolver 630 is coupled to one end of a rotary shaftof a motor 610, and an encoder 620 is coupled to the other end of therotary shaft. In addition, a calculator 640 analyzes output waveforms ofthe resolver 630 and the encoder 620. In detail, after the rotary shaftof the motor 610 is operated, the calculator 640 calculates a rotationangle profile by analyzing the output waveform of the resolver 630 andcalculates an error rate by comparing the rotation angle profile with arotation angle profile of the encoder 620. Each resolver 630 is testedten times, among which a greatest error rate is defined as a maximumerror rate. Generally, the resolver is demanded to have a maximum errorrate of 0.5 or below. The coil occupying ratio is checked by means ofx-ray inspection.

FIGS. 13, 14, 15, 16, 17, 18, 19, 20 and 21 are graphs showing an errorrate of each resolver prepared as a sample, and each graph shows anerror rate according to time in a test where a maximum error rate isfound, when each resolver 630 is tested ten times. FIGS. 13, 14, 15, 16and 17 are graphs respectively showing error rates of Examples 11 to 15of Table 2, and FIGS. 18, 19, 20 and 21 are graphs respectively showingerror rates of Comparative Examples 5 to 8 of Table 2.

Referring to FIG. 13, the resolver of Example 11 has a plus error ratewith a maximum value of 0.3 and a minus error rate with a maximum valueof −0.36. Therefore, the maximum error rate is 0.36 which is an absolutevalue of the minus error rate. Referring to FIG. 14, the resolver ofExample 12 has a plus error rate with a maximum value of 0.32 and aminus error rate with a maximum value of −0.33. Therefore, the maximumerror rate is 0.33 which is an absolute value of the minus error rate.Referring to FIG. 15, the resolver of Example 13 has a plus error ratewith a maximum value of 0.29 and a minus error rate with a maximum valueof −0.29. Therefore, the maximum error rate is 0.29. Referring to FIG.16, the resolver of Example 14 has a plus error rate with a maximumvalue of 0.39 and a minus error rate with a maximum value of −0.42.Therefore, the maximum error rate is 0.42 which is an absolute value ofthe minus error rate. Referring to FIG. 17, the resolver of Example 15has a plus error rate with a maximum value of 0.48 and a minus errorrate with a maximum value of −0.44. Therefore, the maximum error rate is0.48.

Referring to FIG. 18, the resolver of Comparative Example 5 has a pluserror rate with a maximum value of 0.61 and a minus error rate with amaximum value of −0.12. Therefore, the maximum error rate is 0.61.Referring to FIG. 19, the resolver of Comparative Example 6 has a pluserror rate with a maximum value of 0.24 and a minus error rate with amaximum value of −0.52. Therefore, the maximum error rate is 0.52 whichis an absolute value of the minus error rate. Referring to FIG. 20, theresolver of Comparative Example 7 has a plus error rate with a maximumvalue of 0.64 and a minus error rate with a maximum value of −0.21.Therefore, the maximum error rate is 0.64. Referring to FIG. 21, theresolver of Comparative Example 8 has a plus error rate with a maximumvalue of 0.61 and a minus error rate with a maximum value of −0.23.Therefore, the maximum error rate is 0.61.

The above results are listed in Table 2 below.

TABLE 2 maximum occupying ratio shortest distance error rate Example 1132 2.2 0.36 Example 12 32 3.7 0.33 Example 13 32 4.5 0.29 Example 14 374.5 0.42 Example 15 42 4.5 0.48 Comparative Example 5 37 2.2 0.61Comparative Example 6 37 3.7 0.52 Comparative Example 7 42 2.2 0.64Comparative Example 8 42 3.7 0.61

In Table 2, in Examples 11 and 12, it may be found that even though ashortest distance between coils in the slot 112 is less than 4 mm, ifthe coil occupying ratio is 35% or below, the maximum error rate is 0.5or below, which satisfies product requirements. Meanwhile, inComparative Examples 5 to 8, it may be found that if a shortest distancebetween coils in the slot 112 is less than 4 mm and the coil occupyingratio is greater than 35%, the maximum error rate is greater than 0.5,which does not satisfy product requirements.

In particular, if Examples 11 and 12 are compared with Example 13, amaximum error rate when the shortest distance between coils in the slot112 is 4 mm or above and the coil occupying ratio is 35% or below islower than a maximum error rate when the shortest distance between coilsin the slot 112 is less than 4 mm and the occupying ratio is 35% orbelow. In other words, it may be found that the best performance isobtained when the shortest distance between coils in the slot 112 is 4mm or above and the occupying ratio is 35% or below.

In Example 15, it may be found that even though the coil occupying ratiois greater than 35% in the slot 112, if the shortest distance betweencoils is 4 mm or above, the maximum error rate is 0.48 which is lowerthan 0.5 and thus satisfies product requirements. Meanwhile, inComparative Examples 5 to 8, if the coil occupying ratio is greater than35% in the slot 112 and the shortest distance between coils is less than4 mm, the maximum error rate is greater than 0.5 and thus does notsatisfy product requirements.

In other words, if any one of the condition that the shortest distancebetween coils in the slot 112 is 4 mm or above and the condition thatthe coil occupying ratio is 35% or below is satisfied, the resolver hasa maximum error rate of 0.5 or below and thus satisfies productrequirements. Moreover, if both conditions are satisfied, the maximumerror rate is further lower than the case where only one of bothconditions is satisfied, thereby ensuring better performance. Meanwhile,if both conditions are not satisfied, the maximum error rate is greaterthan 0.5 and thus does not satisfy product requirements.

While the present disclosure includes many features, such featuresshould not be construed as limiting the scope of the present disclosureor the claims. Further, features described in respective embodiments ofthe present disclosure may be implemented in combination in a singleembodiment. On the contrary, a variety of features described in a singleembodiment of the present disclosure may be implemented in variousembodiments, singly or in proper combination.

It should be understood by those skilled in the art that manyadaptations, modifications and changes may be made to the presentdisclosure without departing from the technical aspects of the presentdisclosure, and the present disclosure described hereinabove is notlimited by the disclosed embodiments and the accompanying drawings.

What is claimed is:
 1. A resolver, comprising: a stator made of amagnetic material and having a plurality of teeth and a plurality ofslots alternately formed at an inner side thereof; insulation coversrespectively having a tooth insulating unit formed at an inner sidethereof corresponding to the teeth and mounted to the stator at bothupper and lower surfaces of the stator; and coils wound on the teethwith the tooth insulating unit being interposed therebetween, whereinregarding winding widths of coils located at an outermost circumferenceamong the wound coils, a ratio of a shortest winding width to a longestwinding width is 0.69 or above and less than 1; wherein a coil occupyingratio per slot, which is defined by a following equation and representsa ratio of area occupied by the coils in a slot to which the insulationcovers are fixed, is 35% or below: EquationCoil occupying ratio per slot=(area occupied by coils in a singleslot)/(area of a single slot).
 2. The resolver according to claim 1,wherein the ratio of the shortest winding width to the longest windingwidth among the wound coils is 0.8 or above and less than
 1. 3. Theresolver according to claim 1, wherein the coil occupying ratio per slotis 3% to 35%.
 4. The resolver according to claim 1, wherein in a slot towhich the insulation covers are fixed, a shortest distance between coilswound on two teeth adjacent to each other is 4 mm or above.
 5. Theresolver according to claim 1, further comprising: a rotor made of amagnetic material and configured to rotate based on a rotary shaft tochange a gap permeance together with the stator.
 6. The resolveraccording to claim 5, wherein the rotor is ring-shaped having a throughhole formed at a center portion thereof so that the rotary shaft isinserted therein and a plurality of salient poles formed at an outercircumference thereof to change the gap permeance.
 7. The resolveraccording to claim 6, wherein the salient pole has an arc shape with adiameter smaller than at least a diameter of the rotor.
 8. The resolveraccording to claim 7, wherein a center of the arc is disposed spacedapart from a center of the rotor by a predetermined distance, and thearcs of the plurality of salient poles have the same diameter.
 9. Aresolver, comprising: a stator made of a magnetic material and having aplurality of teeth and a plurality of slots alternately formed at aninner side thereof; insulation covers respectively having a toothinsulating unit formed at an inner side thereof corresponding to theteeth and mounted to the stator at both upper and lower surfaces of thestator; and coils wound on the teeth with the tooth insulating unitbeing interposed therebetween, wherein regarding winding widths of coilslocated at an outermost circumference among the wound coils, a ratio ofa mean winding width of the coils located at the outermost circumferenceto a longest winding width is 0.83 or above and less than 1, whereinregarding the winding widths of the coils located at the outermostcircumference among the wound coils, a ratio of the mean winding widthof the coils located at the outermost circumference to a shortestwinding width is greater than 1 and 1.16 or below, and wherein a coiloccupying ratio per slot, which is defined by a following equation andrepresents a ratio of area occupied by the coils in a slot to which theinsulation covers are fixed, is 35% or below: EquationCoil occupying ratio per slot=(area occupied by coils in a singleslot)/(area of a single slot).
 10. The resolver according to claim 9,wherein regarding the winding widths of the coils located at theoutermost circumference among the wound coils, a ratio of the shortestwinding width to the longest winding width is 0.69 or above and lessthan
 1. 11. The resolver according to claim 9, wherein regarding thewinding widths of the coils located at the outermost circumference amongthe wound coils, a ratio of the mean winding width of the coils locatedat the outermost circumference to the longest winding width is 0.89 orabove and less than 1, and wherein regarding the winding widths of thecoils located at the outermost circumference among the wound coils, aratio of the mean winding width of the coils located at the outermostcircumference to the shortest winding width is greater than 1 and 1.1 orbelow.
 12. The resolver according to claim 11, wherein regarding thewinding widths of the coils located at the outermost circumference amongthe wound coils, a ratio of the shortest winding width to the longestwinding width is 0.8 or above and less than
 1. 13. The resolveraccording to claim 9, wherein the coil occupying ratio per slot is 3% to35%.
 14. The resolver according to claim 9, wherein in a slot to whichthe insulation covers are fixed, a shortest distance between coils woundon two teeth adjacent to each other is 4 mm or above.
 15. The resolveraccording to claim 9, further comprising: a rotor made of a magneticmaterial and configured to rotate based on a rotary shaft to change agap permeance together with the stator.
 16. The resolver according toclaim 15, wherein the rotor is ring-shaped having a through hole formedat a center portion thereof so that the rotary shaft is inserted thereinand a plurality of salient poles formed at an outer circumferencethereof to change the gap permeance.
 17. The resolver according to claim16, wherein the salient pole has an arc shape with a diameter smallerthan at least a diameter of the rotor.
 18. The resolver according toclaim 17, wherein a center of the arc is disposed spaced apart from acenter of the rotor by a predetermined distance, and the arcs of theplurality of salient poles have the same diameter.